Hepatitis B is what we used to originally known as just simply serum hepatitis. Hep B has been recognized as this new name since World War II. The virus is responsible for current epidemics in parts of Asia and Africa. Recognized as endemic in China and various other parts of Asia, the Hepatitis B virus has infected over one third of the world's current population.

Hepatitis B is in the Hepadnavirus family. Meaning that it consists of a proteinaceous core particle that has the viral genome inside of it in the form of double stranded DNA. It also has an outside lipid-based envelope that contains embedded proteins. These envelope proteins on the outside are involved in viral binding and release into susceptible cells. Where as the inner capsid refinds the DNA genome to a cell's nucleus where it transcribes viral mRNAs. Although HIV, the virus that causes AIDS, and Hepatitus are not related they are both viruses that use reverse transcription process. This also include HTLV. Hepatitis B's genome is DNA, and reverse transcription is one of the latter steps of the entire process which results in making new viral particles. HIV on the other hand has an RNA genome and reverse transcription is one of the first steps in replication of the virus.

Hepatitis B is most commonly transmitted through direct exposure to bodily fluids that contain the virus. This is a wide category but in most cases includes: - Re-using contaminated needles and syringes - Uncleanly Blood transfusions - Unprotected sexual contact - Direct transmission from mother to child during childbirthThe dominant mode of transmission depends largely on the prevalence of the disease in a given area. For example if areas such as North America drug abuse and unprotected sex are the primary mode of infection. Where as in areas such as such as China where Hepatitis B is very prevalent, the vertical transmission(mother to child) is the most common. A mother who is positive for the Hepatitis B surface virus has a 20% risk of passing the infection to her offspring during birth. That percentage can rise to as high as 90% if the mother is also infected with the hepatitis B e antigen.

The older a person is at the time of infection, the greater the risk that their body will not clear the infection. Hepatitis B infection can lead to a permanent inflammation of the liver, the result of this inflammation leads cirrhosis. These affects largely increase the likelyhood of developing liver cancer.